The use of large format display systems is widely spread and finds applications in control rooms, for advertising, for displaying at events, etc. Most large format display systems used are tiled display systems, constructed out of a number of display tiles or display modules. The latter allows to obtain larger display surfaces than obtainable using conventional displays, by placing a plurality of display tiles adjacent to each other and spread the lighting or imaging output over the different display tiles. The display tiles or modules are mechanically coupled together in order to form the full large format display. The space or gap between the different tiles or modules of the display is called a seam. A plurality of problems are identified in tiled displays, such as for example mechanical stability and strength and imaging or lighting quality near the seams. In U.S. Pat. No. 6,734,617 a tiled flat-panel display is described wherein an increased mechanical stability is obtained by adding stiffening straps at the back of the display modules running across the seams between individual display modules. These redistribute the stress to the straps, thus avoiding damaging of the display system.
In order to obtain a good lighting or imaging quality, the seam should be invisible. Visibility of seams can occur for a number of reasons. One cause of visibility of the seams is the change in pitch between pixels of neighbouring tiles compared to the pitch between pixels of one tile, which is amongst others determined by the alignment of the display tiles. The seam appears as a dark line if the gap between display tiles increases the pitch between individual light sources (e.g. LED's) or pixels at the edge of neighbouring tiles compared to the pitch between individual light sources or pixels within one tile. The seam appears as a bright line at the crossing between display tiles, if the gap between display tiles decreases the pitch between individual light sources (e.g. LED's) at the edge of neighbouring tiles compared to the pitch between individual light sources or pixels within one tile. In the first case the energetic light flux at the mechanical connection of the display tiles decreases, in the second case the energetic light flux increases. Therefore it is advantageous to keep the pitch between individual light sources constant even over the edges of neighbouring tiles. Another cause of visibility of seams between tiles may be the presence of environmental or stray light, e.g. incident on the backside of the tiled display and guided through the seams in the viewing direction.
Some solutions to reduce or avoid these causes of visibility of the seams in tiled display systems have already been provided. For example in US patent application 2002/0163301, a tiled display is described wherein seams between tile modules are filled with optical clear, substantially index matching gap material. The material is adhesive and applied in the seams between the display tile modules. In order to cover the front of the seams, a black patterned coating may be applied to the front of the tiled display, e.g. in a form of horizontal and vertical stripes.